1. Field of the Invention
The present invention relates to an optical scanning system, and more particularly, to an optical scanning technique for a printer, for example, in which an optical scanning unit accurately scans light onto an image print region of a photosensitive belt regardless of track deflection of the photosensitive belt.
2. Description of the Related Art
An earlier optical scanning system comprises an optical scanning unit, a photodetector and an optical scanning controller.
The optical scanning unit having a light source, a rotary optical polygon and a lens unit scans light in a direction perpendicular to the traveling direction of a photosensitive belt, i.e., in a main-scanning direction, along a scanning line on the photosensitive belt traveling around three rollers, and the photodetector is installed at the edge of the photosensitive belt and detects light scanning which has deviated from the photosensitive belt. The optical scanning controller controls the driving of the optical scanning unit according to a pulse signal output from the photodetector in response to the light received by the photodetector.
The light emitted from the light source is reflected by the rotary optical polygon rotating at a predetermined speed. The pulse signal is output to the optical scanning controller in response to the light received by the photodetector. The optical scanning controller determines the end point of the pulse signal as the point in time at which the light emitted from the optical scanning unit reaches the edge of the photosensitive belt, and stops the driving of the light source for a predetermined time duration from the end point of the pulse signal such that the light emitted from the light scanning unit scans from the start point of an image print region on the photosensitive belt. That is, the light does not scan a non-print region of the photosensitive belt. Then, after the predetermined time delay, the light source is driven such that the light scans onto the image print region of the photosensitive belt according to an image signal.
In such operation of the optical scanning system, the duration of the time delay is set based on a normal traveling state where the photosensitive belt travels along a predetermined track.
The scanning speed of a spot of light emitted from the light scanning unit, from a reference point along the scanning line via an edge point on the edge of the photosensitive belt, is different, and such a difference is due to the distances between the light source and each point on the scanning line being different.
In the case where the edge point on the edge of the photosensitive belt is shifted due to an irregular traveling path of the photosensitive belt, that is, where the distance between the reference point and the edge point changes, the light emitted from the light source cannot scan accurately from the start point of the image print region of the photosensitive belt. Because the duration of the time delay is set based on the normal traveling of the photosensitive belt, the start point of the light scanning is deflected, thereby deteriorating the print quality.